Depth measuring system



Nov. 3, 1959 s. G. FISHER DEPTH vMEASURING SYSTEM Filed Sept. 29, 1955 5 Sheets-Sheet 1 Nov. 3, 1959 S. G. FISHER DEPTH MEASURING SYSTEM 5 Sheets-Sheet. 2

Filed Sept. 29, 1955 s R n I- mm l A 232% M Russa Q m M E M S B n ,m m 78m vm l I l| o n n |||||i lll Il Il l| |w l I I l I l l l l l I l I l l I l l I I l l I l l I Q w mi Nov. 3, 1959 s. G. FISHER DEPTH MEASURING SYSTEM 5 Sheets-Sheet 3 Filed Sept. 29, 1955 Nov. 3, 1959 s. G. FISHER 2,910,868

DEPTH MEASURING SYSTEM Filed Sept. 29, 1955 5 Sheets-Sheet 4 .L TRAIN INVENToR. SETH B. FISHER A T TOR/VE YS Nov. 3, 1959 s. G. FISHER 2,910,858

DEPTH MEASURING SYSTEM Filed Sept. 29, 1955 5 Sheets-Sheet 5 Il Il t ll Il sf si l H5 VOLTS 400 "D 3 PHASE INVEN TOR.

(L l l $577! 6. FISHE O O O O O FIG. 5

A T TOR/VE' YS ments, to the UnitedStates of America as represented by the Secretary `of thev Navy Y Application september 29, 1595s, serial No. 537,606

3 claims. (Ci. *ls-301) This invention relates to a measurement of the depth position of a body or a submarine when submerged in a tluid or the sea and the rate of change of the measured depth position when the body is moved to other depths. This application is related to my copending application vSerial No. 537,605, filed September 29, 1955.

Accordingly, an object of the present invention is to indicate accurately the depth position and the rate of change of the depth position of a 4submerged body in a fluid over a wide range of depth.

Another object is to provide an apparatus capable vo high gain and stability with a very quick corrective response tov any change in depth in the position of the the accompanying drawings wherein:

Fig. l shows a block diagram of the apparatus of the invention; p

Figs. 2 through 5 show a schematic'diagram of a preferred embodiment of the apparatus of the invention, wherein; Y g

Fig. 2 is a schematic diagram of the sensing element and balance network;

Fig. 3 is a schematic diagram of the four-stage electronic amplifier; f

Fig. 4 'is a schematic diagram of the magnetic amplivfier, motor, generator, gear train, spiral potentiometer and depth indicator and depth rate indicator; and

Fig; 5 is a schematic diagram of the power supply and transformer.

Referringnow to the drawings, wherein like reference i' jcharacters designate like or corresponding parts, there is Ishown schematically in Fig. .2 a sensing `element and balance network. To solvethe problem of measuring 'the pounds per square inch of static pressure of a uid at any particular depth and converting this measurement lto an indication in feet at that particular depth, a pressure measuring device employing the strain gage principle `connected vas a Wheatstone bridge yas a sensing element is used. For measuring the static' pressure from 0 to 1000 feet of depth, a 0 'to 500 p.s.i.g'. SR-4 Baldwin Fluid Pressure Cell 50 may be used. The voltage output of the cell is caused bythe change in pressure of the uid which varies the resistance of the cell which unbalances the Wheatstone bridge of the sensing element. The output of the Wheatstone bridge is passed through a balance network 60. This network 60 is designed for balancing fz'ero pressure condition fof the cellboth for resist- ,United States Patent lO ice ance and reactance at a-minimum voltage output by potentiometer, pot. 1, and variable capacitors C- and C-2. In addition, the network is capable of adjusting the output of the pressure cell for a minimum (zero) pressure point by pot. 2 and for a maximum (1000 foot) pressure point by pot. 3. The potentiometers pot. 2 and pot. 3 are considered to vbe Calibrating potentiometers. The controlling or spiral potentiometer 140` (Fig. 4) is connected within the balance network 60 and is a ten turn precision potentiometer with negligible capacitances. The function of the spiral potentiometer 140 is to balance the output of the pressure cell at any given pressure for a minimum voltage whose position or value becomes proportional to the depth of the body in the tluid.

The external source ofv 115 volts, 400 cycles, threephase voltage is applied to the transformer 30, power supply V40, motor 90, generator 100, and rate indicator 105. The transformer 30 supplies lament voltage for the electronic amplifier 70 and 8 volts rms, 400 cycle voltage to the pressure cell 50. The pressure of the lluid in which the body carrying the present apparatus is submerged, causes` the resistance of the pressure cell 50 to change which gives la particular output or voltage-per foot of depth. The output of the cell 50 is 7.12 microvolts per foot of depth. In salt water each additional foot of depth increases the static pressure 0.4465 p.s.i.

At a particular depth if the pressure cell 50 is measuring a different depth pressure than is indicated by the ten turn or spiral potentiometer 140, there exists a voltage across the output of the network greater than the balanced minimum voltage for that particular depth. This increased or error voltage is amplified by the electronic amplifier 70, and the magnetic amplifier 80. The speed and direction in rotation of a servo motor is controlled by the output of the magnetic amplifier 80. Servornotor 90 may be of the type known to the Navy as Mk. 12, Mod. 0. The motor is mechanically coupled through a gear train and antibacklash gear train 130 to drive the ten turn potentiometer 140 connected within the balance network so as to decrease this'- error voltage by making the potentiometer indicate the correct value for the particular depth. When the error voltage decreases to a minimum value, servo motor 90 stops and the ten turn potentiometer 140 has been driven to a new position proportional to the static pressure applied to the pressure cell.

By means of adjusting potentiometers, pot. 2 and pot. 3, in the b-alance network, the spiral ten turn potentiometer 140 is adjusted to have a range of a hundred feet of depth error per revolution. By gearing the ten turn potentiometer rotation upwards to the ratio of ten to one and adding a digit counter capable of indicating tenths of a revolution, a vnl lmerical indication of depth in one foot increments is obtained and the counter will thus read directly in feet of depth. With the addition of ten subdivisions between successive numbers, the counter will then indicate tenths of foot of depth.

Since thekabove apparatus for measuring the depth of a position of a body in a iiuid, has a fast responding highly stabilized servo system, the transient response to the error voltage has a short time constant and is well damped. This means that as the static depth pressure changes the system will follow the depth measurement at rates up to the maximum speed of the servo motor with very low error between the indicated depth and the actual depth pressure. As a consequence, the speed of the servo motor is proportional to the rate of change of depth position. There Vis mounted -a 400l cycle generator 100 as an integral part ofv the servo motor 90. The output of this generator is proportional to the speed ofthe motor, therefore, the voltage of this ygenerator becomes a measure of rate of change of depth position. .The polarity of the generated vol-tage indicates the direction of the rate of change of depth position.

`Since A.C. voltmeters are not polarity sensitive, a voltage `of the proper magnitude and phase is added in series with the generator output and this combined voltage is then metered to indicate the rate of change of depth position. The alternating current voltmeter will then be used as a depth rate indicator 105. The meter will indicate zero rate of change of depth position at mid-scale and will indicate an increase for rates of change of depth position producing generated voltages in phase with the fixed voltage and will indicate a decrease for rates of change of depth position producing generated voltages 180 degrees out of phase with the xed voltage of 115 volts, 400 cycles. t

An indication of dual range on the voltmeter or rate indicator 105 is obtained by using the meter 105 with two different voltage ranges and two iixed voltages of different magnitudes as shown by pot. 5 and pot. 6 in Fig. 4. Thus, the rate indicator can be adjusted to indicate depth rates from to 6.5 feet per second climb or dive and from 0 to 2.5 feet per second climb or dive with a linearity and accuracy of :t% of full scale. The maximum value of depth rate can be either increased or decreased by changing the gear ratio between the servo motor and the counter for the depth indication. Remote indication can be accomplished by adding more voltmeters 106 in parallel in a similar manner as shown in Fig. l.

' The measuring system may be a completely contained unit housed in a volume of approximately 14 inches by l2 inches by 7 inches and weighing approximately 20 pounds. All voltages may be obtained within the unit except for 115 volts, three-phase, 400 cycle power. Since the unit weighs little rand uses a strain gage type instead of a Bourdon type sensing element, it is capable of with-l standing shock. This measuring system can be adjusted to indicate depth from 0 feet to 1000 feet with a linearity MiO/5% of full scale and with a resolution of one half foot. 1 The range could beincreased or decreased by selecting a pressure cell with a different range. The linearity could be improved by using a hand calibrated scale to show the position of the ten turn potentiometer 140 instead of the counter. The resolution could be improved by Stringing the resistance of the ten turn potentiometer over 15 or 20 turns. The system could be made to operate on 60 cycles either single-phase or three-phase. Remote depth indication can be added by adding slave counters 'to the present depth counter. The preferred way of adding remote indication as illustrated by Fig. l would be to gear down the ten turn potentiometer rotation by ratio of to l to a synchro generator 160 by an antibacklash gear train 150. This synchro generator could then drive synchro motors 170 that in turn would be geared upward 100 to 1 by an antibacldash gear train 180 and connected to digit counter 190 to show themeasured depth.

In one embodiment of the apparatus of the invention shown merely by way of example and in nowise tobe considered as limiting the scope of the invention, the following values of the various elements were found to be appropriate:

Resistors Ohms Ohms R-l 10K R-12 100K R-Z 9K R-13 33K R-4 200K R-14 12K R-S 33K R-15 390 R-6 18K R 16 510K R-7 100K R-17 220 R-S 120K R-18 220 R-9 33K R-19 510K lR-10 10K R-20 560 R-11 100K t Tubes Chokes Ohms VT1, 2, 3 5744 L-l 3H 225 VT4 5703 L-Z 3H 225 Potentometers Pot. 1 25K ohmsinritial balance. Pot. 2 500 ohms zero foot balance. i Pont. 3A 2.5K ohms foot balance.v `Y Pot. 4 500K ohms depth gain. l Pot. 5 10Kv ohms low rate calibration. Pot. 6 10K ohms high rate calibration. Spiral Pot. 1K ohms.

Condensers C-1 500 mmfd. C-Z V 500 mmfd. C-3 Zmfd.' C-4 Zrnfd: C-S 40 mfd; 450 C-6 40 mfd. -450 WVDC, C-7 n l'mfd. j C-9 Y .01mfd; C-10 .l rnfd. C-11 .01 mfd C-12 .01 mfd' C-13 .5 mf'd It is therefore apparentin the light of the foregoing description that the invention presents a quick, stablleland accurate solution for measuring a depth position and a rate of change for depth position. Y i

Obviously many modiiications and variations of the present invention are possible in the light of the above teachings. It is therefore tobe understood thatwithin the scope of the appended claims the invention may be practiced otherwise than as specicallydescribed.

What is claimed is:` l y y 1. A measuring system for indicating a depth position of a body in a iiuid, comprising a source of alternating voltage, a power supply, a transformer, a iluid pressure cell of strain gage Wheatstone bridge type adapted tol be `unbalanced in accordance with the static pressure of the iiuid at the depth of said body, a network including the fluid pressure cell andan adjustable potentiometergior providing a voltage diiere-nce output corresponding-.to 4the depth position of the body relative to a preselected depth, a servo motor, a iirst gear traincoupled to said servo motor, a digit counter for indicating the depth in feet connected to said first gear train, an antibacklash gear train connected to said first gear train said `potentiometer being connected to said antibacklash gear train, Van `electronic amplifier, a magnetic amplifier, said alternating voltage Isource applied to said input of said power ysupply providing direct current voltage for the tube plates of said electronic ampliiier, said source being impressed upon a windingof said motor, and on saidtransformer for supplying a filament voltage for the tubes of said electronicvampliiier and Vfor supplying the iiuid press/ure cell with a source-of alternating potential, voltage dif,4 ference output provided by said network beingffjed tosaid electronic amplifier, `the voutput of said electronic amplier being fed to said magnetic amplifier, the ,outp,ut of said magnetic amplifier being fed to anotherwindng of said motor inducing the rotation of said 4rotor of said motor, said potentiometer being turned by said. motor through said gear trains to decrease the dierence voltage output to a minimum at which voltage the lservo Vmotor stops, said counter recording the new depth position by the number of turns of said gear train. .n .t

2. The measuring system ofrclaim l1 including a remote depth indicator comprising a second antibacrlglash gear train a synchro generator coupled to saidpotentiometer by'said second antibacklash gear,v train, asynchro motordriven by said synchro generatona third, antiback# lash-gear4 train, and a second digitcountensaid synchro motor driving said third antibacklash gear train and second digit counter to indicate the depth position of a body in a fluid.

3. In a depth measuring system, the combination of a fluid pressure cell having strain gages connected as a Wheatstone bridge as the sensing element for measuring the staticV pressure of a fluid, a modifying network connected to said bridge and having potentiometers for balancing the zero pressure condition of the uid pressure cell both in resistance and reactance Ifor a minimum voltage output of said strain gages and for balancing the output of the strain gages for a minimum voltage over the entire pressure range of said uid pressure cell, one of said potentiometers of said network being a ten turn precision potentiometer having an arm which is positionable to balance the output of the pressure strain gages at any given pressure for a minimum voltage, the arm position of said precision potentiometer being substantially proportional to the depth corresponding to the pressure measured by said strain gages, a four-stage electronic amplifier, said network coupled to the four-stage electronic amplifier, a magnetic amplifier connected to said electronic amplifier, the output difference voltage of said modified bridge at the time the sensing element produces a voltage at a different depth position than that position indicated by the precision potentiometer arm being amplified by said four-stage electronic amplifier the output of said four-stage electronic amplifier being fed to said magnetic amplifier, a servo motor having a control winding, the output of said magnetic amplifier being lfed to the servo motor control winding, gear trains coupled to said precision potentiometer arm, said precision potentiometer arm being turned by said motor through said gear trains to balance the modified bridge in order to produce a difference voltage minimum at which the servo motor stops and the position of said precision potentiometer arm indicates a new depth position, and a digit counter coupled to one of said gear trains to indicate numerically the depth position.

References Cited in the tile of this patent UNITED STATES PATENTS 2,507,304 Hofstadter May 9, 1950 2,689,932 Hornfeck Sept. 2l, 1954 2,729,780 Miller Jan. 3, 1956 

